1. Field of the Invention
The present invention relates to a method of manufacturing an annular member made from a metal sheet used for a pulley or the like, particularly, an annular member made from a metal sheet having a peripheral wall, the peripheral wall has a shape of protruding to either side of a plate-like base portion surrounded by the peripheral wall.
2. Description of the Prior Art
A conventional method of manufacturing this kind of annular member made from a metal sheet, is schematically shown in FIGS. 13 to 15. According to the manufacturing method, a disc-shaped material 1 made from a metal sheet, having a predetermined thickness T3 shown in FIG. 13, is employed thereby manufacturing the member. In other words, the material 1 is held between a pair of dies, not shown in the Figures, thereby rotating the material 1 with the dies, while, against an axial center portion of an outer periphery of the material 1 as shown in FIG. 14, a roller 2 for splitting the outer periphery of the material is pressed to split the outer periphery of the material in a forked state, thereby forming a split portion 3. As shown in FIG. 15, against the split portion 3, a forming roller 4 is pressed, thus forming a peripheral wall 6 protruded on both sides of a non-processed portion 5.
According to the conventional manufacturing method described in FIGS. 13 to 15, the outer periphery of the material 1 is split, thereby forming the split portion 3 which is axially extended to form the peripheral wall 6. As a result, a thickness T3 of the disc-shaped material 1 made of the metal sheet is required to be at least 2 or more times the thickness required to make the peripheral wall 6. In other words, it is required to employ the thick material 1 before forming the peripheral wall 6 of the determined thickness T4, and the thickness T3 of the non-processed portion 5 has the same measurements as the thickness T3 of the original material 1 whereby there is a problem wherein it is difficult to achieve a light weight produced annular member.
Moreover, it is difficult for the thickness T4 of the peripheral wall 6 to be finished so as to be larger than the thickness T3 of the non-processed portion 5. In order to finish it as mentioned above, there has been a problem wherein a thickness disposal of the peripheral wall in a post step must be additionally conducted.